scale nine...in flash

To edit the symbol in flash with scale nine grid ,so that it can be used to skin the flex component, Just do the following :

Whil creating the symbol select the checkbox which says "Enable guides for 9-slice scaling"

The post from the guy behind scale nine in flexcoders :
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Working with rounded corners you'll want to set the left scaleGrid right after the end of the top left curve, for the right scaleGrid set it right before the top right curve starts, for the top scaleGrid set it right after the top left and top right vertical curve ends, and for the bottom scaleGrid set it before the bottom left and bottom right curves start. The artwork inside that "box" or boundaries will be the content that stretches, while everything outside of it will not. ]